A collection of 1920s scenarios and background articles for Call of Cthulhu.

Contains the following scenarios:

- The Auction
- The Madman
- Black Devil Mountain
- The Asylum
- The Mauretania
- Gate from the Past
- Westchester House
- The Curse of Chaugnar Faugn
- Thoth's Dagger

From the back cover:
"The Cthulhu Casebook contains nine independent adventures set in the 1920s, plus numerous articles and aids generating many other plots.

Certain portions of this book are easily included in ongoing tales - 'The Mauretania' can expand any ocean voyage; 'The Asylum' can make exciting and otherwise uneventful institutionalization; 'The Auction' can be used to introduce various artifacts to aid or hinder the investigators.

Other sections contain full independent adventures playable by themselve or useful in filling gaps between campaigns or as subplots within current storylines.